1. Field of the Invention
The present invention relates generally to apparatus for the manufacture of plastic bottles and other similar containers, and particularly to apparatus for the simultaneous manufacture of a large number of containers from preforms according to known general parameters, wherein apparatus is provided for repositioning the preforms which are injection molded at one spacing in preparation for blow molding the preforms to form containers at another spacing.
2. Description of the Prior Art
The production of plastic articles is often facilitated by performing various operations and treatments at a series of work stations, in order to efficiently obtain the desired final articles. As part of performing such operations and treatments, is often the case that the work stations require different relative center spacings of parisons. For instance, where starting material is injection molded to form parisons at an initial work station, close center spacings are often needed due to the difficulty of maintaining the required molten plastic temperature over relatively long flow paths, while at a later work stations, such as a blow molding work station, parisons are expanded, necessitating larger relative center spacings between parisons to permit such expansion. In addition, processing of parisons at later work stations is frequently aided by pairwise disposition of the parisons. As a result, it is often desirable to increase efficiency by increasing the relative center spacings of the parisons from relatively compact, even spacings to relatively extended, paired spacings as the parisons move from one work station to another. The array of available apparatus for repositioning preforms includes apparatus whereby the relative center spacings of a set of parisons disposed in a rectangular array may be varied in a single direction, for example, as described in U.S. Pat. No. 4,197,073, disclosing an apparatus having diverging tracks acting to expand the center spacings of the parisons in a single direction. In addition, apparatus is described in U.S. Pat. No. 4,323,341 whereby parisons are spread in a single direction to accommodate the center spacings required for blow molding, and further, apparatus is described in U.S. Pat. No. 4,313,905 where the relative center spacings of a set of preforms disposed in a linear array may be varied through the use of a carrier block rack having a plurality of angular tines.
Also, there are presently available apparatus for altering the relative spacings, in two directions, between the members of a set of parisons disposed in a rectangular array. A number of embodiments of one such device are described in U.S. Pat. No. 5,273,152. In a first such embodiment, the spreading of parisons between a first center spacing and a second center spacing is controlled by relative movement of the parisons with respect to a guide plate having a plurality of angled grooves. In a second embodiment, a single pantograph scissor unit is employed to expand the parisons in a first direction with the parisons maintained to be evenly spaced, while a piston and rod structure is employed to expand the outer pair of rows of parisons in an orthogonal second direction. In another device, described by U.S. Pat. No. 5,206,039, apparatus for conditioning pressure molded plastic articles is disclosed, and includes a means operative to change the center spacings of parisons between an evenly spaced, compact first center spacing and an evenly spaced, expanded second center spacing, the change in center spacings occurring during movement of the parisons from a pressure molding section to a conditioning section.
Despite the availability of such apparatus, there exists a need in the art for an article repositioning apparatus for altering in two directions the relative center spacings of a set of parisons disposed in a two-dimensional array between an evenly spaced first position and a relatively expanded, paired unevenly spaced second position, for use with an injection stretch blow molding machine for simultaneously molding a plurality of containers from plastic parisons, the machine having a first work station where the parisons are disposed in the first position and a second work station where the parisons are disposed in the second position